Bipolar electrosurgical device with floating-potential electrodes

ABSTRACT

An electrosurgical instrument, system, and methods are provided for the vaporization, cutting, coagulation, or treatment of tissue in the presence of an electrically conductive fluid medium. The electrosurgical probe comprises at least one active electrode, and at least one “floating” electrode having at least one end in close proximity to at least one active electrode. The floating electrode is not connected in any way to the electrosurgical power supply, but rather has a “floating” potential determined by the shape and position of the electrode. The floating electrode increases current density in the region of the probe distal end.

PRIORITY

The instant application is a continuation of U.S. patent applicationSer. No. 10/911,309, filed Aug. 4, 2004, which, in turn, claims thebenefit of provisional application 60/493,729 filed Aug. 11, 2003. Theinstant application also claims priority to U.S. patent application Ser.No. 11/136,514, filed May 25, 2005, which, in turn, claims the benefitof provisional application 60/648,105 filed Jan. 28, 2005. The contentsof these priority applications are incorporated by reference herein intheir entirety.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of electrosurgery,and, more particularly, to high efficiency surgical devices and methodswhich use high frequency (RF) electrical power for cutting, bulk removalby vaporization (ablation), coagulation and treatment of tissue in aconductive liquid environment, as well as other forms of tissuetreatment such as shrinking, lesion formation, sculpting and thermaltreatment with or without externally supplied liquids.

Least invasive surgical techniques have gained significant popularitybecause of their ability to accomplish outcomes with reduced patientpain and accelerated return of the patient to normal activities.Arthroscopic surgery, in which the intra-articular space is filled withconducting fluid, allows orthopedists to efficiently perform proceduresusing special purpose instruments designed specifically forarthroscopists. Among these special purpose tools are various manualgraspers and biters, powered shaver blades and burs, and electrosurgicaldevices. Electrosurgical procedures usually require a properelectrosurgical generator, which supplies the Radio Frequency (RF)electrical power, and a proper surgical electrode (also known as anelectrosurgical probe). Under appropriate conditions the desiredsurgical effects are accomplished.

Note: in common terminology and as used herein the term “electrode” mayrefer to one or more components of an electrosurgical device (such as anactive electrode or a return electrode) or to the entire device, as inan “ablator electrode”. Electrosurgical devices may also be referred toas “probes”.

Arthroscopic electrosurgical procedures rely on the application of RFelectrical power using an electrode (or probe) for cutting, ablation orcoagulation of tissue structures in a joint space which is filled byliquid. Many types of electrosurgical devices can be used, however, theycan be divided to two general categories, monopolar devices and bipolardevices. When monopolar electrosurgical devices are used, the RF currentgenerally flows from an exposed active electrode through the patient'sbody, to a passive, return current electrode that is externally attachedto a suitable location on the patient body. In this way the patient'sbody is part of the return current circuit. When bipolar electrosurgicaldevices are used, both the active and the return current electrodes areexposed, and are typically positioned in close proximity. The RF currentflows from the active electrode to the return electrode through thenearby tissue and conductive fluids. Monopolar and bipolar devices inmany fields of electrosurgery operate according to the same principles.

During the last several years, specialized arthroscopic electrosurgicalprobes called ablators have been developed. Exemplary of theseinstruments are ArthroWands manufactured by Arthrocare (Sunnyvale,Calif.), VAPR electrodes manufactured by Mitek Products Division ofJohnson & Johnson (Westwood, Mass.) and electrodes by OratecInterventions, Inc. (Menlo Park, Calif.), Stryker Corporation(Kalamazoo, Mich.) and Smith and Nephew Endoscopy (Andover, Mass.).These ablators differ from conventional arthroscopic electrosurgicalprobes in that they are designed for the bulk removal of tissue byvaporization in a conductive liquid environment rather than for thecutting of tissue or for coagulation of bleeding vessels.

Recently the use of electrosurgery with conductive fluids for urology,gynecology and other procedures is also becoming popular. Previously,mostly non-conductive fluids were used for these applications.

While standard electrodes are capable of ablation their geometries arenot efficient for accomplishing this task. During ablation water withinthe target tissue is vaporized. Because volumes of tissue are vaporizedrather than discretely cut out and removed from the surgical site, thepower requirements of ablator electrodes are generally higher than thoseof other arthroscopic electrosurgical electrodes. The geometry anddesign of the electrode and the characteristics of the RF power suppliedto the electrode greatly affect the power required for ablation(vaporization) of tissue. Electrodes with inefficient designs willrequire higher power levels than those with efficient designs.

During electrosurgery procedures in conductive fluids, most of the RFenergy delivered to an electrode is dissipated in the fluid and in theadjacent tissue as heat, thereby raising the temperature of the fluidwithin the cavity and of the adjacent tissue. A substantial fraction ofthe RF power is used for the creation of sparks (arcs) in the vicinityof the electrodes. These sparks accomplish the tissue vaporization,cutting and coagulation. In summary, the sparks are essential for tissuevaporization (ablation), while heating of the liquid and tissue awayfrom the active electrode tip always occurs but has no desirableclinical effect.

The heating of the irrigation fluid and especially the adjacent tissueis not beneficial to the patient. On the contrary, this maysubstantially increase the likelihood of patient burns. For this andother reasons, improved, efficient electrosurgical electrodes aredesirable for tissue vaporization and cutting of tissue structures.

An electrosurgical probe, in general, is composed of a metallicconductor surrounded by a dielectric insulator (for example plastic,ceramic or glass) except for the exposed metallic electrode. The probeelectrode is often immersed in a conducting fluid and is brought incontact with the tissue structure during the electrosurgical procedure.The probe is energized, typically at a voltage of few hundred to fewthousand volts, using an RF generator operating at a frequency between100 kHz to over 4 MHz. This voltage induces a current in the conductiveliquid and nearby tissue. This current heats the liquid and tissue, themost intense heating occurring in the region very close to the electrodewhere the current density is highest. At points where the currentdensity is sufficiently high, the liquid boils locally and many steambubbles are created, the steam bubbles eventually insulating part or allof the electrode. Electrical breakdown in the form of an arc (spark)occurs in the bubbles which insulate the electrode. The sparks in thesebubbles are channels of high temperature ionized gas, or plasma(temperature of about a few thousand degrees Kelvin). These high currentdensity sparks, heat, evaporate (ablate) or cut the tissue (depending onthe specific surgical procedure and the probe geometry) that is incontact with the spark.

The spark generation and tissue heating, modification or destructionvery close to the electrode tip are beneficial and desirable effects. Atthe same time the induced current heats the liquid and tissue which is alittle further away from the immediate vicinity of the electrode tip.This heating is undesirable and potentially dangerous because it maydamage tissue structures uncontrollably in surrounding areas and alsodeep under the surface. The design of higher efficiency probes isdesirable as it would lead to less heating of the fluid and tissue notin close proximity, and give the surgeon a larger margin of safetyduring the procedure.

Ablation (vaporizing) electrodes currently in use, whether monopolar orbipolar, have an active electrode surrounded by an insulatorsignificantly larger in size than the ablating surface of the electrode.For ablators with a circular geometry, the diameter of the portion ofthe probe which generates ablative arcs (the “working” diameter) isgenerally not greater than 70 to 80 percent of the diameter of theinsulator (the “physical” diameter) and therefore only about 50% of thephysical probe area can be considered effective. This increases the sizeof the distal end of the electrode necessary to achieve a given ablativesurface size, and necessitates the use of cannulae with relatively largelumens, an undesirable condition.

It is accordingly an object of this invention to produce anelectrosurgical probe which has high efficiency.

It is also an object of this invention to produce an electrosurgicalprobe which has a distal end of compact size.

These and other objects are accomplished in the invention hereindisclosed which is an advanced, high efficiency, electrosurgical probeequipped with an additional one or more metallic electrodes which arenot connected directly to any part of power supply circuit. Thiselectrode may contact the surrounding conducting liquid and/or tissue.The potential of this electrode is “floating” and is determined by thesize and position of the electrode, the tissue type and properties, andthe presence or absence of bodily fluids or externally supplied fluid.This “floating” electrode is mounted in such a way that one portion ofthe electrode is in close proximity to the probe tip, in the region ofhigh potential. Another portion of the floating electrode is placedfurther away in a region of otherwise low potential.

The floating electrode generates and concentrates high power density inthe vicinity of the active region, and results in more efficient liquidheating, steam bubble formation and bubble trapping in this region. Thisallows high efficiency operation, which allows the surgeon tosubstantially decrease the applied RF power and thereby reduce thelikelihood of patient burns and injury.

These innovative electrosurgical devices with floating electrodes may bevery effective in other medical procedures beyond evaporation(ablation), such as, for instance, for thermal treatments, lesionformation, tissue sculpting, and tissue “drilling”, with or withoutexternally supplied liquids.

SUMMARY OF THE INVENTION

An electrosurgical probe is a metallic electrode coated with dielectricexcept for an exposed portion at the electrode tip. This tip is anactive element of the probe. When placed into conductive liquid-tissuemedia and energized, the probe induces electrical current in theconducting liquid and nearby tissue. This current deposits energy intothe liquid and tissue raising their temperatures and creating thedesired clinical effect. The highest energy deposition is in closeproximity to the tip where current density is largest.

Power density in close proximity of the tip depends primarily on theapplied voltage, the shape and size of the exposed portion of theelectrode, and liquid/tissue electrical conductivity. Also it isaffected by the return current electrode size, shape, and position. Ingeneral, positioning the return electrode into closer proximity to theactive electrode increases the power density in the region near theelectrode tip.

In the case of a monopolar probe, the return current is collected by alarge return electrode (sometimes called dispersive electrode or returnpad) placed on the patient's body far away from the probe tip. The powerconcentration capability of a monopolar probe is determined by the shapeof the exposed electrode: the smaller and sharper the tip is, the betterits power concentration capability.

In the case of bipolar probes the return current electrode is placed inmoderate proximity to the active electrode (2-10 mm). Some additionalpower concentration takes place in comparison with the monopolar probewith the same shape of active electrode. The power concentrationcapability can be controlled additionally by the shape and position ofthe return electrode. Decreasing the distance between the returnelectrode and the active electrode increases the power concentration. Aproblem arises when the probe is generating sparks. (Recall that this isthe goal of probe operation in ablation-tissue evaporation or cutting,for example). If the return electrode is placed sufficiently close tothe tip to achieve a substantial increase of power concentration, thebreakdown (arcing within bubbles) takes place between the tip and returnelectrode. The spark conductive channel connects the active electrode tothe return current electrode and the power supply is loaded directly bythe spark. Usually this leads to extra high-energy deposition in thespark between metallic electrodes resulting in localized melting andvaporization of the electrodes themselves. This results in shorting ofthe power supply and destruction of both the active and returnelectrodes with little clinical benefit to the patient.

A good bipolar probe design must avoid arcing between the active andreturn electrodes. Usually this is achieved by placing the returnelectrode a sufficiently large distance away from the active electrodeto prevent direct breakdown between electrodes. Nevertheless, periodicarcing may take place so that both electrodes are eroded and eventuallydestroyed, especially in an aggressive mode of operation. Therefore, theadditional degree of power concentration achievable by bipolar probes isseverely limited.

The subject of this patent application is an electrosurgical device—withone or more additional metallic electrodes which are not connecteddirectly to any part of the power supply circuit, and therefore arecalled “floating”. These floating electrodes are in contact with thetissue or liquid in proximity to the active electrode. The electricalpotential of these additional electrodes is not fixed, but rather is“floating” and is determined by size and position of the electrode andthe electrical conductivity of the tissue/liquid surrounding the distalend of the device. This electrode is positioned in such a way that oneend of the electrode is in close proximity to the active electrode.Another portion of the floating electrode is positioned in a region oflow potential in the liquid. The addition of this floating potentialelectrode thereby substantially modifies the electrical fielddistribution, and energy deposition, in the vicinity of the activeelectrode without the possibility of electrode destruction since thefloating electrode is not directly connected to the electrical powersupply. This is demonstrated by two-dimensional numerical modeling, asshown in FIGS. 74 through 80. In the figures a section view through aprobe distal tip is shown. Only the top half of the tip is shown. Thetip is symmetrical about the bottom of the figure. In FIGS. 74 and 76,the energy deposition around an electrosurgical electrode with a single,cylindrically symmetric floating potential electrode is shown. FIG. 76is an expanded view of the region in which the floating and activeelectrodes are in close proximity. In FIGS. 75 and 77 the energydeposition around a similar probe tip without a floating electrode isshown. FIG. 77 is an expanded view of the region in which the activeelectrode meets the insulator. The presence of the floating electrodeconcentrates the intensity over the physical area of the electrode. Thisis in contrast to the probe without a floating electrode, in which theenergy density is concentrated around the active electrode only. FIG. 79shows the power deposition around an electrosurgical probe with afloating electrode and as well as a return electrode on the probe incontact with the conductive fluid. FIG. 80 is an expanded view of theregion of the probe of FIG. 79 in which the floating electrode andactive electrode are in close proximity. FIG. 81 shows the powerdeposition in the region surrounding the active electrode of a probelike that shown in FIG. 79 but without a floating electrode. It isimportant to note that the floating electrode concentrates the power inthe vicinity of the active electrode when the return is mounted on theprobe in the same manner that it concentrates power when a remotelyplaced return electrode is used (for example, when a return electrode isexternally attached to the patient's body).

In the absence of sparking (arcing within bubbles) this electrodeincreases power density in the vicinity of the probe tip. This isbecause the floating electrode extends from a high potential region(near the active electrode), to a region with low potential (fartherfrom the active electrode), and “shorts” these points together. Theprobe floating potential will be in between the potentials of thesepoints. The presence of the electrode decreases the potential near theactive electrode, therefore increasing the electric field, current andpower density in the region near the active electrode. A floatingelectrode works about the same way as any extended conductive object inthe electrostatic field. The higher power density results in moreefficient liquid heating and steam bubble formation, which allows one todecrease the power applied to probe for a given effect. In the presenceof the “floating” electrode more sparks are generated in the activeregion, since this region is larger. Bubble trapping is greatly enhancedwith proper design of the floating electrode, insulator and the activeelectrode.

Sparks are an active element of an electrosurgical process. A spark isgenerated in a steam bubble if the bubble field (voltage differenceacross a bubble) is sufficient for breakdown. Usually sparks aregenerated in bubbles that are close to the active electrode of the probebecause current density and field intensity are largest in this region.

The breakdown or spark inside a bubble is an electrically conductivechannel of partly ionized pressurized gas. This medium is called highlycollisional plasma. The basic property of this plasma is that theconductivity is proportional to the plasma density. Higher plasmatemperatures are associated with higher ionization rates, plasmadensities and conductivity.

Usually energy is deposited into highly collisional plasmas by electriccurrent driven by voltage applied to electrodes at the ends of a plasmachannel. In the case of a plasma channel formed inside of a bubble, theinner parts of the bubble surface with the largest voltage differenceact as the electrodes to which the channel is connected. Mostfrequently, but not always, one of these electrodes is a metallicsurface of the active electrode and the other is the opposite surface ofthe bubble or the surface of the tissue.

Electrically, the plasma channel is characterized by its impedance. Theefficiency of energy deposition strongly depends on the ratio betweenthe plasma channel and the power supply impedance. Efficiency (theportion of applied energy deposited to the plasma) as high as 50% can beachieved for matched conditions in which the power supply impedanceequals the spark (plasma channel) impedance. If the channel impedance istoo large or too small, the power deposition in the plasma is decreased.The power source for the plasma channel formation is the step voltagecreated by current flow in the conductive liquid surrounding the bubble.The effective impedance of the power supply is of the same order as theimpedance of liquid with dimensions of a bubble. That means that themaximum power deposited into the arc channel is on the order of thepower deposited into a volume of the bubble size filled with liquid.Deviation of the channel impedance from its optimum value results indecreased power deposition into the channel. These principles are validif at least one of channel electrodes is the inner liquid surface ofbubble.

The energy which is deposited to a plasma channel (spark) is determinedby the energy density in the surrounding conductive liquid. As taughtpreviously herein, the additional metallic “floating” electrodedescribed in this patent application significantly increases the energydensity in the region surrounding the active electrode. This makes itpossible to substantially increase the power deposited into the spark.Since the floating electrode can be placed very close to the probe tip,the largest probability is for breakdown and plasma channel formation inthe region between the two metallic electrodes—the active electrode andthe floating potential electrode. The plasma channel current can now besupported not by a bubble size fraction of the induced current, but by amuch larger volume of current flow that is determined by the size offloating electrode. This floating electrode additionally concentratescurrent delivered to the spark. The optimum spark current can becontrolled by adjusting the size and position of the floating electrode.Arcing, then, can occur through bubbles between the active and floatingelectrodes, or from either electrode through bubbles in contact with anelectrode.

In summary, the subject of this invention is an advanced,electrosurgical probe equipped with an additional “floating potentialelectrode”. The floating electrode concentrates the power (i.e.increases the power density) in the active region, which leads to moreefficient liquid heating, steam bubble formation, and spark generationin this region. The floating electrodes also strengthen the entire probeassembly by protecting the insulator (made of a ceramic or otherdielectric). A properly designed floating electrode will favorablyeffect bubble formation and trapping, and therefore will enhance theprobe's performance. This results in high efficiency operation, allowingthe surgeon to substantially decrease the applied RF power, or shortenthe procedure time, and thereby reduce the likelihood of patient burnsand injury, while at the same time maintaining high performanceoperation. Arcing occurs from the floating electrode as well as theactive electrode resulting in a probe in which the distal tip has a“working” diameter equal to the “physical” diameter in the case ofprobes having a radial symmetry. This is in contrast to an electricallyactive area normally being only about 50% of the physical area of thedevice.

In some embodiments the probes have a radial symmetry with the floatingelectrode forming the outermost radial surface at the probe tip. Thefloating electrode may completely or only partially surround the tip,and may have features to locally increase the current density such as,for instance, notches or protuberances. In other embodiments the probetip has a non-radial symmetry with the floating electrode completely orpartially surrounding the active electrode, while in other embodimentsthe floating and active electrode form an array of protuberances withthe floating electrodes being interspersed in the array of activeelectrodes. In yet other embodiments the active and floating electrodesform an assembly having a blade-like structure useful for cuttingtissue.

The active and floating electrodes may be formed and arranged in avariety of configurations to accomplish tissue vaporization for a rangeof applications and conditions. These include, but are not limited to,bulk tissue vaporization, tissue cutting, and producing holes in tissue.Because the field is intensified, the time required to form steambubbles and achieve arcing within the bubbles is shortened.

The current invention is useful also for medical procedures in whichtissue is thermally treated rather than removed by vaporization, suchas, for instance, cardiology, oncology and treatment of tumors,sometimes referred to as lesion formation. In these applications thedevice is brought into close proximity, or contact, with tissue with orwithout the presence of externally applied conductive fluid at the sitefor thermal treatment. The voltage applied to the active electrode isreduced to a level which produces current densities insufficient forforming sparks and the associated bubbles. Tissue is heated to a desiredtemperature for a predetermined time sufficient for lesion formation.The floating electrode intensifies the electric field in the regionsurrounding the active electrode so as to produce a larger, morecontrolled and more uniform lesion.

Some probes used for thermal treatment have geometries designed forheating without the forming of the bubbles which lead to arcing andtissue vaporization. In these embodiments it is desirable to have a moreuniform current density at the active and floating electrodes.Accordingly, features such as notches, grooves, ribs or protuberances,for locally increasing the current density are absent. The active andfloating electrodes may be, for instance, rings displaced axially on aprobe shaft, either a single active and single floating electrode, ormultiples of either the active electrode or floating electrode, ormultiples of both. The active and floating electrodes may completely, oronly partially surround the probe tip.

The innovative approach of incorporating a floating electrode (orelectrodes) for the concentration of power in the active area may beadvantageously applied to probes used with remotely located returnelectrodes, and to probes having a the return electrode located on theprobe itself (in the vicinity of the active area).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an electrosurgical system, including anpower supply, a dispersive (return) electrode, wiring, and anelectrosurgical probe constructed in accordance with the principles ofthis invention.

FIG. 2 is a plan view of an arthroscopic ablator electrode made inaccordance with the principles of this invention.

FIG. 3 is a side elevational view of the objects of FIG. 1.

FIG. 4 is a perspective view of the object of FIG. 1.

FIG. 5 is an expanded plan view of the active electrode at the distalend of the object of FIG. 1.

FIG. 6 is a side elevational view of the object of FIG. 5.

FIG. 7 is a perspective view of the object of FIG. 5.

FIG. 8 is a plan view of the insulator at the distal tip of the objectof FIG. 1.

FIG. 9 is a front elevational view of the object of FIG. 8.

FIG. 10 is a plan view of the floating electrode at the distal tip ofthe object of FIG. 1.

FIG. 11 is a front elevational view of the object of FIG. 10.

FIG. 12 is a plan view of the tip assembly of the object of FIG. 2 withthe dielectric coating removed.

FIG. 13 is a front elevational view of the object of FIG. 12.

FIG. 14 is a perspective view of the object of FIG. 12.

FIG. 15 is an expanded plan view of the distal end of the object of FIG.1.

FIG. 16 is a side elevational view of the objects of FIG. 15.

FIG. 17 is a perspective view of the objects of FIG. 15.

FIG. 18 is an expanded perspective view of the far distal portion of theobjects of FIG. 15 schematically showing current flow paths in theregion of the active and floating electrodes.

FIG. 19 is an expanded perspective view of the far distal portion of theobjects of FIG. 15 schematically showing bubble and arc formation in theregion of the active and floating electrodes.

FIG. 20 is a side elevational view of the distal end portion of analternate embodiment having a chamfered ring electrode.

FIG. 21 is a perspective view of the object of FIG. 20.

FIG. 22 is a side elevational view of the distal end portion of analternate embodiment having an extended active electrode.

FIG. 23 is a perspective view of the object of FIG. 22.

FIG. 24 is a side elevational view of the distal end portion of analternate embodiment having an extended floating electrode.

FIG. 25 is a perspective view of the object of FIG. 24.

FIG. 26 is a plan view of the distal end portion of an alternateembodiment having slots in the floating electrode.

FIG. 27 is a side elevational view of the object of FIG. 26.

FIG. 28 is a perspective view of the object of FIG. 26.

FIG. 29 is a plan view of the distal end portion of an alternateembodiment having a ribbed active electrode.

FIG. 30 is a perspective view of the object of FIG. 29.

FIG. 31 is a side elevational view of an alternate embodiment havingadditional exposure of the floating electrode in the low-potentialregion of the electric field.

FIG. 32 is a perspective view of the object of FIG. 31.

FIG. 33 is a side elevational view of an alternate embodiment similar tothe object of FIG. 31 but with radial slots formed in the floatingelectrode.

FIG. 34 is a perspective view of the object of FIG. 33.

FIG. 35 is a perspective view of an alternate embodiment distal assemblyhaving an increased portion of the floating electrode in thelow-potential region of the electric field.

FIG. 36 is a perspective view of the object of FIG. 35 with a first halfof the floating electrode removed.

FIG. 37 is a plan view of the objects of FIG. 36.

FIG. 38 is a side elevational view of the objects of FIG. 36.

FIG. 39 is a plan view of an alternate embodiment in which the activeelectrode forms a plurality of protuberances.

FIG. 40 is a perspective view of the object of FIG. 39.

FIG. 41 is a plan view of an alternate embodiment in which the activeelectrode forms a plurality of protuberances, and the floating electrodeis forms a planar surface through which the protuberances protrude.

FIG. 42 is a perspective view of the object of FIG. 41.

FIG. 43 is a perspective view of an alternate embodiment in which theactive and floating electrodes form a plurality of protuberancesarranged in a rectangular array.

FIG. 44 is a side elevational view of the object of FIG. 43.

FIG. 45 is a bottom view of the object of FIG. 43.

FIG. 46 is a plan view of the object of FIG. 43.

FIG. 47 is a side elevational sectional view of the object of FIG. 43along the centerline of the object.

FIG. 48 is a perspective view of an alternate embodiment havingelongated active and floating electrodes.

FIG. 49 is a side elevational view of the object of FIG. 48.

FIG. 50 is an end sectional view of the object of FIG. 48.

FIG. 51 is a perspective view of an alternate embodiment withaspiration.

FIG. 52 is an expanded perspective view of the distal end of the objectof FIG. 51.

FIG. 53 is a plan view of the object of FIG. 51 with a first halfremoved.

FIG. 54 is a side elevational view of the object of FIG. 53 showing theaspiration path.

FIG. 55 is an expanded view of the distal end of an alternate embodimentwith aspiration.

FIG. 56 is a perspective view of an alternate embodiment with anelectrode assembly formed to a blade shape.

FIG. 57 is an expanded perspective view of the distal end of the objectof FIG. 56.

FIG. 58 is a side elevational view of the object of FIG. 57.

FIG. 59 is an expanded side elevational view of the object of FIG. 57.

FIG. 60 is a distal end sectional view of the object of FIG. 59.

FIG. 61 is an expanded distal end sectional view of the object of FIG.59 during use.

FIG. 62 is an expanded view of the distal portion of an alternateembodiment having the electrode assembly formed to a blade shape.

FIG. 63 is a side elevational view of the object of FIG. 62.

FIG. 64 is an expanded distal-end sectional view of the object of FIG.63.

FIG. 65 is a perspective view of an alternate embodiment configured toproduce holes in tissue.

FIG. 66 is a plan view of the object of FIG. 65.

FIG. 67 is an expanded perspective view of the distal end of the objectof FIG. 65.

FIG. 68 is an expanded side elevational view of the object of FIG. 65.

FIG. 69 is a side elevational view of the distal portion of the objectof FIG. 65 during use.

FIG. 70 is a perspective view of an alternate embodiment configured toproduce holes in tissue, and having a means for supplying conductiveliquid to the probe tip.

FIG. 71 is an expanded plan view of the distal end of the object of FIG.70.

FIG. 72 is an expanded side sectional view of the distal end of theobject of FIG. 70.

FIG. 73 is an expanded side sectional view of the distal end of theobject of FIG. 70 during use.

FIG. 74 is a plot of the power density in the region surrounding thedistal end of an electrosurgical probe with a floating electrodesubmerged in a conductive liquid.

FIG. 75 is a plot of the power density in the region surrounding thedistal end of an electrosurgical probe submerged in a conductive liquid.

FIG. 76 is an expanded plot of the power density in the regionsurrounding the active electrode of an electrosurgical probe with afloating electrode submerged in a conductive liquid.

FIG. 77 is an expanded plot of the power density in the regionsurrounding the active electrode of an electrosurgical probe submergedin a conductive liquid.

FIG. 78 is a plot of the power density in the region surrounding thedistal end of an electrosurgical probe having a return electrode mountedon the probe, and having a floating electrode, submerged in a conductiveliquid.

FIG. 79 is an expanded plot of the power density in the regionsurrounding the active electrode of the probe with a return electrodemounted on the probe and a floating electrode shown in FIG. 78.

FIG. 80 is an expanded plot of the current density in the regionsurrounding the active electrode of a probe with a return electrodesubmerged in a conductive liquid.

DESCRIPTION OF THE EMBODIMENTS

Referring to FIG. 1, electrosurgical system 700 has an electrosurgicalpower supply 702, an electrosurgical probe 1 with electrical cord 6, anda dispersive (return) electrode 704 with electrical cord 706.

Referring FIGS. 2 through 4, probe 1 has a proximal portion 2 forming ahandle and having a proximal end 4 from which passes electrical cord 6,and a distal end 8 which attaches to proximal end 10 of elongated distalportion 12. Distal portion 12 has a distal end 14 and a tubular portion16. Tubular portion 16 has a proximal end 17 and a distal end 18.Buttons 7 and 9 control the RF power applied to the probe.

Distal end 14 is an assembly having an active electrode, a ringelectrode, a ceramic or other dielectric insulator placed between theactive and ring electrodes, and a dielectric coating which covers atleast a portion of the distal end assembly. The distal end assembly andits components are shown in FIGS. 5 through 17.

Referring to FIGS. 5 through 7, active electrode 20 has a proximal end22 and a distal end 24. Proximal end 22 forms a longitudinal cylindricalportion 26 having a diameter 27 slightly larger than the lumen of distalend 18 of tubular portion 16 (FIGS. 2 through 4) such that electrode 20can be assembled to tubular portion 16 using a press fit. Cylindricalportion 28, coaxial with portion 26, has a diameter 29 approximatelyequal to the outer diameter of distal end 18 of tubular portion 16.Distal end 24 has an upper cylindrical portion 30 and a lower coaxialcylindrical portion 32. The axis 34 of cylindrical portions 30 and 32and the axis 36 of proximal cylindrical portion 26 form an angle 38.Angle 38 is 90 degrees in the example shown. Angle 38 may be in therange from 0 to 90 degrees. Upper cylindrical portion 30 of diameter 40and length 42 has a recessed cylindrical pocket 44 of diameter 45 in itsupper surface so as to form a rim 46 of width 48. Lower cylindricalportion 32 has a diameter 49. Proximal end 22 and distal end 24 arejoined by elongated portion 50 which has a rectangular cross-section,although other cross-sections may be used. Electrode 20 is manufacturedby machining from bar stock or, more preferably by metal injectionmolding. Electrode 20 is made of a suitable metallic material such as,for instance, stainless steel, nickel, tungsten or titanium.

Referring to FIGS. 8 and 9, insulator 60 has a cylindrical tubular formhaving an upper portion 62 of diameter 64 and length 66 and a lowerportion 68 of diameter 70 and length 72. Inner diameter 74 of insulator60 is slightly larger than diameter 40 of upper cylindrical portion 30of active electrode 20. Diameter 70 of lower portion 68 is approximatelyequal to diameter 49 of lower cylindrical portion 32 of active electrode20. Insulator 60 is made of a suitable dielectric material such as, forinstance, alumina or zirconia.

Referring to FIGS. 10 and 11, ring electrode 80 has a cylindricaltubular form having an inner diameter 82 approximately equal to diameter64 of upper portion 62 of insulator 60, and an outer diameter 84approximately equal to diameter 70 of lower portion 68 of insulator 60.Ring electrode 80 has a length 86.

As seen in FIGS. 12 through 14, distal end subassembly 90 is formed ofactive electrode 20, insulator 60, and ring electrode 80. Insulator 60is mounted to active electrode 20 such that upper portion 30 ofelectrode 20 protrudes through insulator 60 as shown, portion 30protruding above insulator 60 distance 91. Ring electrode 80 isassembled to mounted insulator 60 such that the top surface of ringelectrode 80 is approximately equal in height to active electrode 20with insulator 80 forming an annular recess 92 between them. Subassembly90 is assembled to distal tip 18 of tubular portion 16 as shown.

Referring now to FIGS. 15 to 17, distal end assembly 14 is formed bysubassembly 90 and dielectric coating 94. Coating 94 covers elongateddistal portion 12 and subassembly 90 except for the region includingmost of ring electrode 80, the exposed upper surface of insulator 60,and the portion of active electrode 20 which protrudes from insulator60. More specifically, coating 94 covers lower end 96 of ring electrode80 so as to leave an exposed portion 98 having a top end 100 and bottomend 102. Coating 94 is made from a suitable polymeric material which maybe applied, for instance, as a powder coat or liquid which issubsequently cured, or as a molded or extruded tube which is shrunk byheat after application. Components of subassembly 90 are held in placeby coating 94, although a suitable adhesive cement may also be used.

As seen in FIG. 18, during use, distal end 14 of probe 1 is submerged ina conductive liquid. Return electrode 704 is applied to the patient at asite remote to the surgical site. Radio Frequency (RF) energy issupplied to active electrode 20 creating an electric field in theconductive fluid. Top end 100 of exposed portion 98 of ring electrode 80is in a high-potential region of the electric field. Bottom end 102 ofportion 98 of electrode 80 is in a lower potential region of theelectric field. Current flows from rim 46 of active electrode 20 intothe conductive fluid, the current density being greatest immediatelyadjacent to the exposed surface of rim 46. Some current 104 flows intothe fluid and through the patient's body to the return electrode.Current 106 flows through the conductive liquid to high-potential topend 100 of ring electrode 80, through electrode 80 to lower potentialregions of exposed portion 98 near bottom end 102. Current 106 flowsfrom the lower potential regions of electrode via the conductive fluidto the patient's body and return pad 704. Electrical current passingthrough conductive fluid heats the fluid, making it more conductive,which in turn causes more current to flow through the heated region.Probe 1 shown in FIG. 18 has two regions of high current density, thefirst at rim 46 of active electrode 20 and the second at top end 100 ofring electrode 80. As seen in FIG. 19, heating of the conductive liquidin these areas causes it to boil forming bubbles 108 on rim 46 ofelectrode 20 and bubbles 110 on top end 100 of ring electrode 80. Arcs112 occur within some of these bubbles. When distal end 14 of ablator 1is brought into contact with, or close proximity to tissue, some of thebubbles intersect the tissue surface and arcs pass from the electrodes,through the bubbles to the tissue, which is ablated (vaporized).

Numerous modifications may be made to distal tip 14. For instance, FIGS.20 and 21 show an embodiment in which top end 122 of ring electrode 120is chamfered so as to form a top surface 124 of reduced area for thepurpose of achieving higher current density at the ring electrode. FIGS.22 and 23 show an embodiment in which active electrode 130 protrudesbeyond ring electrode 132 a distance 134. FIGS. 24 and 25 show anembodiment in which ring electrode 140 is protrudes beyond the top endof active electrode 142 a distance 144. FIGS. 26 through 28 show anembodiment in which a plurality of slots 150 are formed in top end 152of the ring electrode 154. Slots 150 decrease the exposed area at thetop of electrode 154 thereby increasing the current density in theregion. Slots 150 also produce a plurality of edges which concentratecurrent so as to increase bubble generation. Similarly, the embodimentshown in FIGS. 29 and 30 has an alternate active electrode configurationhaving a plurality of slots for the purpose of concentrating current atthe edges formed thereon so as to enhance bubble formation. Activeelectrode 160 has multiple slots 162 formed in top surface 164.

In another embodiment, the ring electrode is increased in size so as toplace a larger area of the electrode in the low potential region of theelectric field created by the active electrode. Referring now to FIGS.31 and 32, distal tip assembly 170 is similar to that of the previousembodiments. That is, an active electrode is separated from a concentricring electrode by an insulator. The assembly is covered by a dielectriccoating except for selected portions of the distal tip. Active electrode172 is separated from ring electrode 174 by insulator 176. Ringelectrode 174 is approximately equal in length to the distal cylindricalportion of active electrode 172. Dielectric coating 178 covers assembly170 as on the previous embodiments except that a second portion 180 ofextended ring electrode 174 is left uncoated. When assembly 170 issubmerged in conductive liquid and RF energy is supplied to activeelectrode 172, upper end 182 of ring electrode 174 is in ahigh-potential region of the electric field. Portion 180 of ringelectrode 174 is in a low-potential region of the electric field. Thecurrent path during use is the same as that for the previous embodimentsexcept that current now flows from the larger exposed portion 180 ofring electrode 174 into the conductive liquid for return to thegenerator via the dispersive pad. The larger exposed area in thelow-potential region of the electric field results in higher currentdensities at the portion of the ring electrode in the high-potentialregion of the electric with a resulting increase in ablator efficiency.

In another embodiment based on the embodiment of FIGS. 31 and 32, slotsare formed in the ring electrode so as to reduce the area of the portionof the electrode in the high-potential region of the electric field soas to increase the current density in that portion. Edges formed by theslots create regions of high current density with further aid bubbleformation. Referring to FIGS. 33 and 34, distal assembly 194 isconstructed in the same manner as the embodiment of FIGS. 31 and 32except that top end 200 of ring electrode 196 has a plurality of slots198 formed therein, the axial depth 201 of the slots being greater thandistance 202 that ring electrode protrudes beyond coating 204.Accordingly, top end 200 of ring electrode 196 forms a plurality ofprotrusions 206 which protrude from the top surface 208 of coating 204.

Other constructions of the distal tip are possible which allow furtherincrease in the size of the portion of the floating electrode which isin the low-potential part of the electric field. An embodiment with sucha construction is shown in FIG. 35.

Referring to FIG. 35, assembly 214 attaches to distal end 14 of tubulardistal portion 16 (FIG. 1) in the same manner as the previousembodiments and has attached a floating electrode 220 made of anelectrically conductive material such as, for instance, stainless steel.Electrode 220 is formed of identical but symmetrically opposite firsthalf 222 and second half 224 joined by, for instance, laser welding.Electrode 220 has a proximal end 226 and a distal end 228, end 226 beingpressed into distal end 14 of tubular distal portion 16 of ablator 1.Distal end 228 of electrode 220 forms a cylindrical portion 230 having arim 232. Centered within portion 230 is active electrode 234 separatedfrom portion 230 by insulator 236.

Referring now to FIGS. 36 through 38, active electrode 234, insulator236, conductor rod 238, and dielectric coating 240 together form aninner assembly 242 located within electrode 220 and electricallyisolated therefrom. Insulator 236 has a larger diameter upper portion244 and a smaller diameter lower portion 246 which locates insulator 236within cylindrical opening 248 of second electrode half 224. Upperportion 244 has formed therein cylindrical pocket 250. Active electrode234 has a larger diameter upper portion 252 having a diameter slightlyless than the diameter of cylindrical pocket 250 of insulator 236 sothat electrode 234 may be mounted therein. Electrode 234 has a smallerdiameter lower portion 254 which protrudes through lumen 256 ofinsulator 236, portion 254 having a lateral cylindrical opening 258 intowhich is assembled distal end 260 of conductor rod 238. Rod 238, theportion of electrode 234 protruding beyond the bottom end of insulator236, and the bottom end of insulator 236 are covered by dielectriccoating 240. A dielectric coating (not shown) covers elongated distalportion 12 (FIGS. 2 through 4) while leaving a predetermined portion ofelectrode 220 uninsulated, the portion being optimized so as to maximizethe electric field intensity at rim 232.

In the embodiments heretofore described the floating electrodecompletely surrounds the active electrode. In certain circumstances itmay be desirable to intensity the field in only a portion of the probetip. In these embodiments the floating electrode only partiallysurrounds the active electrode. In other embodiments two or morefloating electrodes are used, the floating electrodes locallyintensifying the portion of the field in which they are formed.

In another embodiment shown in FIGS. 39 and 40, the active electrode hasa plurality of protuberances 260 which protrude from an insulator 262surrounded by floating electrode 264. Dielectric coating 266 covers tipassembly 270 except for exposed portion 268 of floating electrode 264.FIGS. 39 and 40 show an assembly in which protuberances 260 are all ofequal height and are approximately equal in height to floating electrode264. Protuberances 260 may vary in height. For instance, those towardthe center of the array may be of greater height than those at theperiphery so as to increase tissue engagement by the center of theprobe. Also, some or all of protuberances 260 may be of greater orlesser height than floating electrode 264 to achieve a desired ablativeeffect.

Another embodiment shown in FIGS. 41 and 42 has a distal tip assembly280 in which floating electrode 282 is a cylindrical element having aplurality of axial cylindrical holes therethrough. Active electrode 284has a plurality of protuberances 286 protruding from the axialcylindrical holes in floating electrode 282, and electrically isolatedfrom floating electrode 282 by insulator 288 which has tubular portions290 surrounding protuberances 286. Current flow 296 is fromprotuberances 286 through the conductive liquid to axial surface 292 offloating electrode 282 in the high potential portion of the electricfield, through floating electrode 282 to portion 294 of electrode 282which is in a lower potential portion of the electric field, and thenthrough the conductive fluid to the return. In FIGS. 41 and 42,protuberances 286 are of equal height. The protuberances may be ofdiffering heights in order to achieve a given ablative effect, such as,for instance, to have either the peripheral or central portion of thearray preferentially engage tissue.

In the embodiments shown in FIGS. 39 through 42, all protuberances areat the same electrical potential, and were surrounded by an annular orplanar floating electrode. In another embodiment shown in FIGS. 43through 47, distal tip assembly 300 has a plurality of protruding pinelectrodes 304 and 306. Pins 304 are connected to each other and areconnected to the power supply so as to be active electrodes. Pins 306are floating electrodes connected to plate 308 which forms bottomportion 310 of distal end 312 of assembly 300. As best seen in FIG. 47,insulator top half 314 and bottom half 316 together form an assemblywhich isolates active electrodes 304 and floating electrodes 306.Dielectric coating 318 covers proximal portion 320 of assembly 300.

In yet another embodiment shown in FIGS. 48 through 50, distal tipassembly 330 has an active electrode 332 forming a plurality of ribs334, and a channel-shaped floating electrode 338 separated by insulator336. Proximal portion 340 of assembly 330 is covered by a dielectriccoating. In another embodiment, a portion of floating electrode 338 iscoated with a dielectric coating so as to increase current density atthe portions of electrode 338 in close proximity to active electrode332. Upper ends 342 of electrode 338 may be chamfered to decrease thewidths of ends 342 to locally increase the current density.

During electrosurgery in a liquid filled space, tissue is vaporizedproducing steam bubbles which may obscure the view of the surgeon ordisplace saline from the region of the fluid filled space which thesurgeon wishes to affect. In the case of ablation (vaporization), thevolume of bubbles produced is even greater than when using otherelectrodes since fluid is continually boiling at the active electrodeduring use. Ideally, flow through the joint carries these bubbles away,however, in certain procedures this flow is frequently insufficient toremove all of the bubbles. In such cases it is desirable for theelectrode to have an aspiration means which removes some bubbles as theyare formed by the ablation process, and others after they have collectedin pockets within the joint. An ablator probe with aspiration generallyhas at least one port located at the probe distal end which is connectedvia a lumen to an external vacuum source which provides suction forbubble evacuation.

FIGS. 51 through 54 show an embodiment of the current invention having ameans for aspiration, and a means for controlling the aspiration flow.As seen in FIG. 51, electrosurgical probe 400 has a proximal portion 402forming a handle and having a proximal end 404 from which passeselectrical cord 406 and tube 407, and a distal end 408 which attaches toproximal end 410 of elongated distal portion 412. Distal portion 412 hasa distal end 414 and a tubular portion 416. Tubular portion 416 has aproximal end 417 and a distal end 418. Distal end 414 of distal portion412 has located therein aspiration port 411 in communication with tube407 via a flow path formed by a lumen within tubular portion 416, and aflow conduction means within proximal portion 402. Slide 413 controlsaspiration flow through probe 400. Buttons 403 and 405 control the RFpower applied to probe 400.

Referring now to FIGS. 52 through 54, distal end assembly 414 of ablator400 is identical in construction to assembly 214 of the ablatorembodiment shown in FIGS. 35 through 38. Accordingly, only thosefeatures unique to the aspiration assembly 414 of ablator 400 will bedescribed. As best seen in FIG. 52, electrode 420 of assembly 414 has inits top surface, proximal to the active electrode, aspiration port 411.As best seen in FIGS. 53 and 54, aspiration port 411 is in communicationwith an aspiration passage formed by the inner portion of electrode 420and the lumen of tubular portion 416. Inner assembly 442 is electricallyisolated by dielectric coating 420 from fluid and materials flowingthrough the passage.

During use, suction supplied by an external vacuum source via tube 407to probe 400 evacuates fluid, bubbles and debris from the surgery site,the rate of flow being controlled by slide 413.

In another alternate embodiment (see FIG. 55) the aspiration port islocated at the distal end of the assembly. Assembly 514 is identical inconstruction to assembly 14 shown in FIGS. 15 through 17. Aspirationport 516 in distal end 518 of assembly 514 communicates via a lumenhaving a dielectric coating with the lumen of tube 512, from which theflow path is identical to that of the embodiment of FIGS. 52 through 54.The aspiration functions in the same manner as the previous embodiment.

The placement of the aspiration port affects the manner in which bubblesare removed from the surgery site. For instance, assembly 414 willaspirate heated fluid and bubbles which are in close proximity to thetop surfaces of the active and floating electrodes, and in doing so maylower the temperature of the fluid in the region thereby affecting theablation performance and efficiency. Aspiration using the port placementof assembly 514 will have less effect on the temperature of the fluidsurrounding the top surfaces of the active and floating electrodes andwill therefore have less effect on the ablation process. Otherplacements of the aspiration port may also be used. In another alternateembodiment the aspiration port is placed in the ablating surface of theactive electrode, with aspiration flow being via a lumen through theactive electrode to the lumen of the distal tubular portion of theprobe. Such placement allows the aspiration of bubbles directly from theablation site, although flow must be carefully controlled to maintainacceptable ablation efficiency due to the likely removal of some processheat rather than waste heat by the aspiration flow. In yet anotherembodiment the aspiration port is in the region between the active andfloating electrodes.

The use of a floating electrode to concentrate the energy field isuseful for other configurations of electrosurgical devices as well. Analternate embodiment shown in FIGS. 56 through 60 has a blade-likedistal portion for use in cutting tissue. Electrosurgical probe 600 hasa proximal portion 602 forming a handle and a distal portion 604.Proximal portion 602 has buttons 606 and 608 for controlling an RF powersupply connected to probe 600 by cord 610. As best seen in FIGS. 57through 60, distal assembly 620 has an elongated flat first metallicmember 622 forming a floating electrode, and a second metallic member624 forming an active electrode and surrounding the perimeter of firstmember 622, members 622 and 624 being separated and electricallyisolated by dielectric member 626. Second member 624 is connected byinsulated wires 628 to the RF power supply such that when button 606 or608 is depressed the appropriate output is supplied to active electrode624. Dielectric member 626 is made of a suitable polymeric or ceramicmaterial able to withstand high operating temperatures. As best seen inFIG. 60, second metallic member 624 has a perimeteral edge formed to awedge shape having an included angle 630, and is made of a suitablematerial such as, for instance, stainless steel, nickel, tungsten orniobium. In another embodiment member 624 is a formed wire, anddielectric member 626 has a channel formed in its perimeteral surface,member 624 being positioned partially within the channel.

Referring now to FIG. 61 showing probe 600 during use, when assembly 620is cutting tissue, an electric field is formed around active electrode624. Floating electrode 622 has a region 632 near its perimeter in closeproximity to active electrode 624 which is in the high-intensity regionof the electric field, and a region 634 in a lower intensity region ofthe electric field. The effective “shorting together” of the regions ofthe electric field by the floating electrode intensifies the field inthe region between the active electrode and the perimetral portion ofthe floating electrode causing increased heating in the region. Currentflow during use is generally from the active electrode to the returnelectrode (dispersive pad) placed on the patient's body at a distancefrom the surgery site. The path taken will be determined by the locationwithin the region surrounding assembly 620. A portion of the current 640flows from active electrode 624 via arcs in gap 636 to the tissue andthrough the tissue to the return electrode. Arcing in gap 636 vaporizestissue thereby enlarging the gap in the direction of the probeadvancement. Another portion of the current 642 in the region in closerproximity to floating electrode 622 flows from active electrode 624through gap 636 to the tissue, through the tissue to portion 632 offloating electrode 622 in the high-intensity region of the electricfield, through floating electrode 632 to portion 634 in the lowerintensity region of the electric field, and from portion 634 into thetissue and via the tissue to the return electrode.

When a standard uninsulated blade-type electrode is used to cut tissue,current flows from all uninsulated surfaces in contact with tissue orconductive liquid, the liquid being either supplied as irrigant orbodily fluids. In areas of high current density arcing causesvaporization of tissue. In areas of low current density tissue iscoagulated and desiccated. Heating of the electrode by these processescauses charred tissue residue to adhere to the sides of the electrodethereby decreasing its efficiency. Probe 600, in contrast, has an activeelectrode 624 of limited surface area such that during use all of thesurface in proximity to tissue or conductive liquid will have highcurrent density. Dielectric member 626 serves as a thermal as well aselectric insulator. Accordingly, active electrode 624 is subjected tovery high temperatures which tend to vaporize tissue in contact with itand therefore have minimal buildup of tissue residue. Floating electrode622 has high current densities and high temperatures in portion 632 ofthe electrode in close proximity to active electrode 624, and lowercurrent density in the portions 634 of electrode 622 in the lowintensity regions of the electric field. Accordingly, the overalltemperature of floating electrode 622 is much less than that of astandard blade electrode and the buildup of tissue residue is diminishedor eliminated.

Other constructions of a blade-like distal assembly are possible. FIGS.62 through 64 show a blade-like distal assembly formed from laminations.Assembly 650 has a first metallic member 652 which is electricallyconnected via a handle and cable to an electrosurgical generator so asto form an active electrode. Member 652 has a perimeter region 664 whichprotrudes beyond dielectric laminations 654 and 656 distance 658. Secondmetallic members 660 and 662 are electrically isolated from firstmetallic member 652 and form floating electrodes, not being connected tothe electrosurgical power supply. Operation of the embodiment of FIGS.62 through 64 is identical to that of FIGS. 56 through 60. Becausemember 652 protrudes beyond dielectric members 654 and 656 around theentire perimeter of assembly 650 the electrosurgical instrument may beused to cut in a forward or backward direction, or advanced distallyinto tissue. This may not always be desirable. For instance, for addedsafety in some situations it may be desirable to have only one activeedge which will cut tissue. Embodiments are anticipated in which onlyselective portions of the active electrode are exposed, the remainingportions being surrounded by a dielectric member and, in some cases, aportion of the floating electrode.

Electrosurgical probes with radial symmetry constructed in accordancewith principles of the invention described herein have an effectiveactive diameter equal to the physical diameter of the working portion ofthe ablator. That is, the floating electrode (the portion of the ablatorof largest diameter) becomes active, forming bubbles and arcs whichvaporize tissue. This is in contrast to other electrosurgical devices inwhich the active electrode is surrounded by a larger diameter insulator.Because the devices of this invention have an active area equal to theirphysical area they can be advanced into tissue in a directionperpendicular to the ablating surfaces, creating in the tissue a selfsupporting channel much in the manner of a drill. This is not possiblewith other probes which have a working diameter less than their physicaldiameter. With these probes significant advancement into tissue isprevented by the physical size of the insulator.

A probe constructed in accordance with the principles of this inventionfor producing holes in tissue is shown in FIGS. 65 through 68. As bestseen in FIGS. 65 and 66, probe 800 is similar in construction to othernon-aspirating embodiments herein described having a proximal handleportion 802 with buttons 804 and 806 for controlling and electrosurgicalpower supply to which it is connected by cable 808. Distal portion 810has a distal tip assembly 812. Referring now to FIGS. 67 and 68, distaltip assembly 812 has an active electrode 814 separated by insulator 816from floating electrode 818. Dielectric coating 820 covers a proximalportion of insulator 816, a proximal portion of active electrode 814,and the rest of distal portion 810.

Referring now to FIG. 69, during use electrode 800 is advanced distally830 into the tissue, the distal surfaces of the active electrode (notshown) and distal surface 822 of floating electrode 818 having currentdensity sufficient to cause vaporization of tissue. Bubbles 824 andproducts of the vaporization are expelled proximally through gap 826formed between distal assembly 812 and the tissue. Lower current densityheating from the more proximal region 824 of floating electrode 818desiccates tissue with which it is in contact so as to stop bleeding.The site may be submerged in a conductive liquid, conductive liquid maybe supplied to the site as an irrigant, and conductive bodily fluids maybe utilized in the hole making process.

In certain circumstances, such as when making holes with large depth todiameter ratios, it may be desirable to supply conductive fluid to theprobe distal end. An embodiment incorporating such a fluid supply meansis shown in FIGS. 70 through 72. Electrosurgical probe 840 is similar inconstruction to probe 800, probe 840 having a proximal handle portion842 with buttons 844 and 846 for controlling an electrosurgical powersupply to which it is connected by cable 848. Distal portion 850 has adistal tip assembly 852. Tube 880 is connected to a source of conductiveliquid which is supplied via a means in handle 842 and a lumen in distalportion 850 to distal tip assembly 852. Control means 882 regulates theamount of liquid supplied to tip assembly 852. Referring now to FIGS. 71and 72, distal tip assembly 852 has an active electrode 854 separated byinsulator 856 from floating electrode 858. Dielectric coating 870 coversa proximal portion of insulator 856, a proximal portion of activeelectrode 854, and the rest of distal portion 850. Lumen 872 suppliesconductive liquid 884 to distal end 874 of active electrode 854 and theregion surrounding electrode 854, insulator 856 and the distal end offloating electrode 858.

Referring now to FIG. 73, during use probe 840 is advanced distally intothe tissue, distal surface 888 of active electrode 854 and distalsurface 892 of floating electrode 858 having current density sufficientto cause vaporization of tissue. Conductive liquid 890 supplied by lumen872 fills the region surrounding the probe tip and helps flush bubbles864 and products of tissue vaporization proximally through gap 866formed between distal assembly 852 and the tissue. Lower current densityheating from the more proximal region 867 of floating electrode 858desiccates tissue with which it is in contact so as to stop bleeding.

The embodiments previously herein described are used with a returnelectrode affixed to the patient at a remote location. These embodimentsmay be modified by adding a return electrode to the probe so as tocreate other embodiments which are also within the scope of thisinvention. The intensification of the power in the active region occursregardless of the location of the return electrode.

Heretofore the applications for electrosurgical probes constructed inaccordance with the principles of the invention described herein havebeen for the vaporizing of tissue. The current invention is useful fornon-vaporizing applications such as lesion formation also. For such usethe voltage applied to the probe is limited so that the maximumtemperatures generated are below the boiling point of water. Thisprevents steam bubble formation and the associated arcing within thebubbles. When forming a lesion on a surface or inside the bulk of thetissue (interstitial) the size of the lesion formed is strongly affectedby the size and shape of the electrode, the level of the applied power,and the duration for which power is applied. It is necessary to applysufficiently high power to form a lesion, but still not too high inorder to avoid vaporization and or tissue charring. The heating effectof an electrode surface in contact with tissue is nonuniform with highercurrent density and heating at and near the perimeter of the surface.Lesions produced by such electrodes are also nonuniform.

When using an electrosurgical probe of the current invention tothermally treat tissue, the probe distal end is positioned such that theactive electrode and floating electrode are both in contact with thetissue at the site for lesion formation. A voltage is applied to theactive electrode to cause heating of the tissue in contact with theactive electrode sufficient to cause lesion formation, but below thethreshold needed for vaporization. Current flows from the activeelectrode into the tissue. Some current goes directly through the tissueto the return electrode. A portion of the current goes from the activeelectrode to the portion of the floating electrode which is in closeproximity in the high-intensity region of the electric field. Thiscurrent flows through the floating electrode and exits in thelow-potential portion of the electrode to flow through conductive fluidor tissue with which this portion of the floating electrode is incontact to the return electrode. The portion of the floating electrodein close proximity to the active electrode has regions of high currentdensity and therefor heating sufficient to cause lesion formation.Accordingly, for a given power level it is possible to create a largerand more uniform lesion using a probe of the current invention than whenusing a standard probe.

The electrosurgical probe having a floating electrode as taught hereinmay be employed for a variety of arthroscopic procedures, for example,in the dissection, resection, vaporization, desiccation and coagulationof tissue structures in various endoscopic and percutaneous proceduresperformed on joints of the body.

The electrosurgical device of the present invention may be also used inhysteroscopic surgical procedures or urological endoscopic(urethroscopy, cystoscopy, ureteroscopy and nephroscopy) andpercutaneous interventions. Hysteroscopic procedures may include:removal of submucosal fibroids, polyps and malignant neoplasms;resection of congenital uterine anomalies such as a septum or subseptum;division of synechiae (adhesiolysis); ablation of diseased orhypertrophic endometrial tissue; and haemostasis. Urological proceduresmay include: electro-vaporization of the prostate gland (EVAP) and othersimilar procedures commonly referred to as transurethral resection ofthe prostate (TURP) including, but not limited to, interstitial ablationof the prostate gland by a percutaneous or perurethral route whetherperformed for benign or malignant disease; transurethral or percutaneousresection of urinary tract tumors; division of strictures as they mayarise at the pelviureteric junction (PUJ), ureter, ureteral orifice,bladder neck or urethra; correction of ureterocoele, among others.

The electrosurgical device of the present invention may be also be usedadvantageously in ENT (ear, nose, throat) for treating tonsils and upperairways obstruction, as well as for GI, oncology and cardiology.

Indeed, the present invention may be used advantageously in virtuallyall fields of electrosurgery.

1. A bipolar electrosurgical probe comprising: a. a shaft having aproximal end and a distal end; b. at least one active electrode locatedat or near the distal end of said shaft, wherein said at least oneactive electrode is connected to a power supply; c. a conductorconnected to said at least one active electrode; d. a return currentelectrode disposed on the shaft in moderate proximity to the at leastone active electrode; e. at least one conductive member disposed at thedistal end, wherein said at least one conductive member comprises afloating electrode that is not connected to a power supply; and f. adielectric member disposed between the at least one active electrode andthe at least one conductive member, wherein said at least one conductivemember has a distal portion and a proximal portion with the distalportion being positioned in close proximity to an end of the at leastone active electrode so as to concentrate the power in the vicinity ofthe active electrode and increase the energy density in the regionsurrounding the active electrode.
 2. The probe of claim 1 wherein saidat least one active electrode and said return current electrode areseparated by a distance of about 2 to 10 millimeters.
 3. The probe ofclaim 1 wherein said at least one active electrode and said at least oneconductive member are separated by a distance of about 0.1 to 10millimeters.
 4. The probe of claim 3 wherein said at least one activeelectrode and said at least one conductive member are separated by adistance of about 0.2 to 4 millimeters.
 5. The electrosurgical probe ofclaim 1 wherein said at least one active electrode and the distalportion of said at least one conductive member protrude beyond an end ofthe dielectric member.
 6. The electrosurgical probe of claim 1 whereinsaid distal portion of said at least one conductive member extendsbeyond a distal portion of said at least one active electrode.
 7. Theelectrosurgical probe of claim 6 wherein said distal portion of said atleast one conductive member is tapered.
 8. The electrosurgical probe ofclaim 6 wherein said distal portion of said at least one activeelectrode is angled.
 9. The electrosurgical probe of claim 1 whereinsaid distal portion of said at least one conductive member is adjacentto a proximal portion of said at least one active electrode.
 10. Theelectrosurgical probe of claim 1 wherein said distal portion of said atleast one conductive member extends between a distal and proximalportion of said at least one active electrode.
 11. The electrosurgicalprobe of claim 1 wherein said at least one conductive member comprises aplurality of protuberances.
 12. The electrosurgical probe of claim 1wherein said at least one active electrode comprises a plurality ofprotuberances.
 13. The electrosurgical probe of claim 12 wherein saidprotuberances comprise a plurality of ribs separated by grooves.
 14. Theelectrosurgical probe of claim 1 wherein said at least one activeelectrode forms an annulus with the at least one conductive member. 15.The electrosurgical probe of claim 1 wherein said at least oneconductive member comprises an annular ring disposed about said at leastone active electrode.
 16. The electrosurgical probe of claim 1 whereinsaid at least one active electrode and said at least one conductivemember form an array of protuberances in which the active and floatingelectrodes are interspersed.
 17. The electrosurgical probe of claim 1wherein said distal portion of said at least one conductive member formsa distal surface, said surface comprising a plurality of lumens, andsaid protuberances passing through said lumens and protruding distallybeyond the distal surface.
 18. The electrosurgical probe of claim 1wherein said dielectric member is made from a refractory material. 19.The electrosurgical probe of claim 1 further comprising a means forsupplying conductive fluid to the shaft distal end.
 20. Theelectrosurgical probe of claim 19, wherein said means for supplyingconductive fluid comprises at least one lumen disposed along the lengthof said shaft, said lumen having a first port disposed at the proximalend of said shaft and a second port disposed at the distal end of saidshaft.
 21. The electrosurgical probe of claim 1 further comprising ameans for aspirating liquid and ablation products from the region of theprobe distal end.
 22. A method for thermally treating tissue at a siteon a patient comprising the steps of: providing the bipolarelectrosurgical probe according to claim 1; positioning a distal end ofsaid probe in close proximity to tissue to be ablated; submerging thedistal end of said probe in a conductive liquid; and applying highfrequency voltage between said at least one active electrode and saidreturn electrode to heat a portion of the tissue.
 23. The method ofclaim 22 in which said conductive liquid is bodily fluids from thepatient.
 24. The method of claim 22 in which said conductive liquid isirrigant supplied to the region surrounding said distal end of saidprobe.
 25. The method of claim 22 in which said conductive liquidsubstantially fills a natural or created cavity in the body of apatient.
 26. The method of claim 22 wherein the portion of tissue isheated to a degree to permit vaporization.
 27. A system for theelectrosurgical ablation or thermal treatment of tissue comprising: a.an electrosurgical generator; b. a bipolar electrosurgical probeaccordingly to claim 1; and c. cabling connecting said monopolarelectrosurgical probe to said generator.